Cobalt base oxidation resistant alloy

ABSTRACT

A COBALT BASE, CHROMIUM-CONTAINING ALLOY HAVING MINOR AMOUNTS OF SILICON AND LANTHANUM CHARACTERIZED BY EXCELLENT OXIDATION RESISTANCE AT TEMPERATURES OF 1200*C. AND HIGHER. THE INCLUSION OF SMALL OF MANGANESE IN THE ALLOY FURTHER ENHANCES THE OXIDATION RESISTANCE OF THE ALLOY.

July 6, 1971 Filed Nov. 4, 1968 WEIGHT GAIN mg/cm H. HATWELL ETA!- COBALT BASE OXIDATION RESISTANT ALLOY 5 Sheets-Sheet 1 CoCrNi (A) CoCrNiLa (B) CoCrNiSi (c) Co-Cr-Ni-Si-Mn-La (E) Co-Cr-Ni-Si-La (0) 3 0 4 o s o I 0F EXPQSUREHQURS FIG.|

INVENTORS ATTORNEY July 6, 1971 HATWELL ETAL 3,591,371

COBALT BASE OXIDATION RESISTANT ALLOY I Filed Nov. 4, 1968 3 Sheets-Sheet a a oe 240' TIME HOURS FIG. 2

10 20304050 60 TOBOQOIOO l I. g In OQQFDMQMN- NW9 lHQlHM INVENTORS HENRI HATWELL CHARLES |D.DESFORGES P E L. MOENTACK BY ATTORNEY July 6, 1971 HATWELL ETAL 3,591,371

COBALT BASE OXIDATION RESISTANT ALLOY Filed Nov. 4, 1968 3 Sheets-Sheet 8 "Z I I l I I I ll i- T=a12 c FIG. 3

0.17% Elongation per minute O u R 3 E 2 as C d o L- m 25 1 l 1 l l l l l 1 $0 a e a a o o ww/m SSHHIS rusuzu INVENTORS RI HATW HEN ELL CHARLEES D. DESFORGES PIER L. MOENTACK BY 14% ATTORNEY United States Patent M 3,591,371 COBALT BASE OXIDATION RESISTANT ALLOY Henri Hatwell, Indianapolis, Ind., and Charles D. Desforges, Rhode-St.-Genese, and Pierre L. Moentack, Brabant, Belgium, assignors to Cabot Corporation Filed Nov. 4, 1968, Ser. No. 773,149 Int. Cl. C22c 19/00 US. Cl. 75-171 4 Claims ABSTRACT OF THE DISCLOSURE A cobalt base, chromium-containing alloy having minor amounts of silicon and lanthanum characterized by excellent oxidation resistance at temperatures of 1200 C. and higher. The inclusion of small of manganese in the alloy further enhances the oxidation resistance of the alloy.

This invention relates to cobalt base alloys suitable for use at elevated temperatures and in oxidizing environments. More particularly, the present invention is directed to chromium-containing cobalt base alloys characterized by excellent oxidation resistance at temperatures of 1200 C. and above.

Cobalt base alloys have been employed in the past in high temperature applications on account of their advantageous mechanical properties under such conditions but on account of their rather poor resistance to oxidation at high temperature the use of such alloys has been severely restricted. In particular, the oxidation of cobalt base alloys (and also that of the generally more oxidation resistant nickel base alloys) has been extremely poor at temperatures of 1200 C. and above. This situation is unfortunate since at the present time there are many applications, e.g. jet aircraft engine components, in which cobalt base alloys could be used to great advantage if the oxidation resistance of these alloys, at temperatures of 1200 C. and above, could be improved.

It is therefore an object of the present invention to provide a highly oxidation resistant cobalt base alloy.

It is another object of this invention to provide a cobalt base alloy characterized by excellent resistance to oxidation at temperatures of 1200 C. and above.

Other objects will be apparent from the following description and claims taken in conjunction with the drawing in which FIGS. 1 and 2 show comparative oxidation data in the form of graphs for various alloys including alloys in accordance with the present invention, and

FIG. 3 shows, in the form of a graph, mechanical data for an alloy of the present invention.

A cobalt base alloy in accordance with the present invention contains at least 35% Co and about:

Percent Cr 1-5-25 Ni -35 Si 0.1-1.0

W 3 La 0.02-0.3

Alloys in the foregoing compositional range have been found to have excellent oxidation resistant properties at high temperatures.

In a preferred embodiment of the present invention, the alloy additionally contains manganese in an amount up to about 2% and is characterized by a further improve- 3,591,371 Patented July 6, 1971 ment in oxidation resistance under cyclic conditions, and improved mechanical properties. The preferred manganese content is from about 0.4 to 1%.

As part of the present invention, it has been discovered that cobalt base alloys containing from about 15 to 25% chromium can be remarkably improved in oxidation resistance at high temperatures by the addition of both silicon and lanthanum in controlled amounts when the tungsten content of the alloy is kept below about 3%. For further improvement in oxidation resistance the tungsten content should be less than 1% and for optimum results the tungsten content should be less than 0.1%, and preferably the alloy is tungsten-free.

Also, as previously mentioned, the inclusion of manganese in amounts up to about 2% further enhances the oxidation resistance.

A particularly preferred alloy compositional range in accordance with the present invention is as follows:

Percent Cr 1 8-24 Si 0.2-0.4 La 0.09-0.15 Mn 0.3-0.6 W 0.05 Ni 18-24 Co Balance A specific preferred alloy composition is 20% Cr, 0.3 Si, 0.1% La, 0.5% Mn, Ni, balance Co.

In addition to the constituents previously mentioned, the alloy of the present invention can contain minor amounts of elements ordinarily present in commercial cobalt base alloys. For example, iron can be present up to about 10% and molybdenum up to about 1%, however it is preferred that the alloy be essentially free of molybdenum.

To demonstrate the advantages of the present invention, extensive testing of various alloys was conducted, including isothermal and cyclical thermal oxidation tests in dry air.

The isothermal tests involved exposing alloy samples to flowing dry air at a constant temperature and recording the weight gain of the samples as a function of time. The samples were in the form of hot rolled sheet 2 mm. thick. Before testing the samples were solution treated for one hour at 1080 C. in argon and quenched in brine.

The compositions of the alloys are shown in Table I below:

TABLE I Alloy composition, percent by weight 1 Balance.

In the isothermal oxidation testing of the above alloys at 1100 C., it was found that alloys D and E, in accordance with the present invention, were superior. The results are shown in the graph of FIG. 1.

Further isothermal oxidation tests were conducted at 1200 C. and these results are shown in the graph of TABLE II.OXIDATION DATATHERMAL CYCLING FOR 100 HOURS Metal con- A M, sumption,

Alloy lug/0111. mg./cm.

F 6.15 (average)-.. 15. 2 E- -0.6 (average) 4.8

Further tests were made at different temperatures to determine mechanical properties for the alloy of the present invention. The results of these tests for alloy E (20% Cr, 0.34% Si, 0.1% La, 0.62% Mn, 20% Ni, balance Co) are shown in the graph of FIG. 3. The samples tested were prepared by being hot rolled to sheet 0.1 mm. thick, solution treated for 30 minutes at 1100 C. and water quenched. The testing was performed in air.

As can be seen from FIG. 3, the mechanical properties of the alloy of the present invention, in conjunction with its oxidation characteristics, shows its suitability as a matrix metal for composite materials.

What is claimed is:

1. A cobalt base alloy having excellent resistance to oxidation at high temperatures, especially at about 1200 C. or higher, containing at least 35% by weight of cobalt and consisting essentially, in proportions by weight, of about:

Percent Chromium 15-25 Nickel 15-35 Silicon 0.1-1.0 Lanthanum 0.020.3 Tungsten 3 with balance basically being cobalt.

2. An alloy in accordance with claim 1 containing up to 2% manganese by weight and less than 1% each of tungsten and molybdenum by weight.

3. An alloy in accordance with claim 1 consisting essentially of about:

Percent Chromium 18-24 Nickel 1 8-24 Silicon 0.20.4 Lanthanum 0.09-0.15 Manganese 0.3-0.6 Tungsten 0.0-5 Cobalt (basically) Balance 4. An alloy in accordance with claim 1 consisting es sentially of about:

Percent Chromium 20 Nickel 20 Silicon 0.3 Lanthanum 0.1 Manganese 0.5 Cobalt Balance References Cited UNITED STATES PATENTS 2,247,643 7/1941 Rohn et al 75-171 3,418,111 12/1968 Herchenroeder 75--171 RICHARD O. DEAN, Primary Examiner 

